Molucca Sea Plate
My Blogs (olelog) are mainly based on my daily reading of earth science news.
Here on whatonearth.olehnielsen.dk I try to weave some of the pieces together to a greater whole with added background info.
The Molucca Sea Plate is a micro plate squeezed in between the micro plates: Sangihe Plate and Malmahera Plate, all three in Indonesia. The Molucca Sea is the only present day example of ocean basin closure as a result of subduction of oceanic lithosphere in two opposite directions. The outcome of the double subduction has been the creation of the Sangihe arc in the west and Halmahara arc in the east.
Tectonic setting based on a map from USGS showing a major earthquake in the Molucca Sea Plate on Sunday 21 January 2007
The Molucca Sea is an active earthquake area.
The Molucca Sea Plate was originally part of the Philippine plate when the Australian Plate was much further south 13 million years ago. The Sangihe trench was active at that time, subducting oceanic lithosphere of the Molucca Sea to the west. The Sangihe subduction is believed to date back to the Oligocene and is much older than the Halmahera in the west. The depth of the downgoing slab at the Sangihe subduction zone is therefor much deeper than at at the Halmahera subduction zone (see diagram). The Sangihe Arc will continue to override the Halmahera arc and in 5 Ma the Molucca Sea will eventually disappear. In the north it has in fact already disappeared under the Eurasian Plate and The Philippine Sea Plate, as most of the Molucca Sea Plate has already been "consumed" (subducted) by the Halmahera subduction zone in the east and by the Sangihe subduction zone in the west.
Volcanic activity along the Halmahera arc has ceased north of Morotai Island, but volcanism continues further north along the opposite Sangihe arc.
The Sorong Fault Zone is a major left-lateral fault system separating Australia from the Philippine Sea Plate (Halmahera micro plate) and the Molucca Sea Plate.
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